1. Field of the Invention
The present invention relates to a wavelength conversion apparatus and a wavelength conversion method which convert the wavelength of incident laser light, and a laser light generating apparatus including such a wavelength conversion apparatus.
2. Description of the Related Art
Among nonlinear optical crystals used for converting the wavelength of laser light, a BBO (beta barium borate; β-BaB2O4) crystal and a CLBO (CsLiB6O10) crystal are used specifically for converting the wavelength of a high-frequency wave (short wavelength), and they often receive laser light in a deep ultraviolet region. Therefore, when the nonlinear optical crystals are used for a long time, the nonlinear optical crystals are damaged to cause a decline in wavelength conversion efficiency.
Therefore, to allow the nonlinear optical crystals to keep high wavelength conversion efficiency for a long time, various techniques have been proposed in related art. For example, Japanese Unexamined Patent Application Publication No. H10-268367 has proposed a method of moving a nonlinear optical crystal. Moreover, for example, Japanese Unexamined Patent Application Publication No. 2006-30594 has proposed a method of increasing the longevity of a nonlinear optical crystal by adjusting the angle of the nonlinear optical crystal in addition to moving the nonlinear optical crystal. Further, Japanese Unexamined Patent Application Publication No. 2006-317724 has proposed a method of reducing output fluctuation by increasing the number of times a nonlinear optical crystal is moved to reduce the movement amount of the nonlinear optical crystal.